First Paragraph:
To what extent do electoral systems determine party systems?
Are plurality electoral systems invariably dominated by two
parties? Under what conditions is Duverger's law true? These
are central questions in the study of electoral politics,
and of critical concern to countries currently employing
plurality rules as well as to others who may be
contemplating a switch to a more majoritarian system.

First paragraph in the conclusion:Without deprecating the role of minor party leaders and
activists (at the margins, leadership certainly matters) it
may be put forth as a general hypothesis that minor party
performance is endogenous to major party performance. Minor
parties owe their successes or failures more to cracks in
the armor of the major parties than to their own efforts
(Schattschneider, 1942, 1960). Indeed, over the long haul
(ignoring the results of particular elections and electoral
periods), minor parties are best considered as a
characteristic of a polity, rather than of a particular
group or grievance. The level of success that these protest
groups achieve over time - the equilibrium result of a party
system - is a system-wide phenomenon. Where the major
parties are doing their job, rumblings of discontent should
be coopted (or if you prefer, represented) by one or both of
these established institutions. It is only when they fail to
perform this representative function, or when their
performance is purely rhetorical (and hence not credible),
that minor parties have a good opportunity to win seats in a
plurality electoral system.